Spur gear teeth with an involute profile on a typical pair of parallel axis drive gears have reduced sensitivity to centering distance between the parallel axes. The contact stress of the spur gear teeth, however, increases from the pitch circle toward the top and bottom lands. Spur gear teeth on the typical pair of parallel axis gears with a constant relative radius of curvature section have a relatively constant contact stress from the pitch circle toward the top land and the bottom land but have increased sensitivity to centering distance of the parallel axes.